That sounds like quite the experience! I've gone on a few vipassana retreats that were quite intense, but it is where I got the most "in touch" with my inner self and my local mindfulness community. I'll have to look up what zazen entails!
Mindfulness as a category is so broad in my experience. I work with kids in middle school, and while those that are able to focus on small practices seem to be benefit it's difficult to provide something deeper within a 1-hr format where I'm also supposed to meet specific treatment goals. I totally agree that much of the stuff printed is pretty worthless, when I take the time to engage and show what mindfulness does is when it is most effective.
I'm glad you found something that works well for you!